Scrubber water waste is a dilute caustic soda (sodium hydroxide) and water solution effluent waste which is formed, for example, in commercial processes for the manufacture of polyolefins such as polypropylene and particularly the step of cracking condensates from natural gas.
After use, the scrubber water waste presents a significant disposal problem since it is highly alkaline, usually containing approximately 3 to 8 percent by weight of sodium hydroxide. Also, scrubber water wastes usually contain soluble sulfides, typically in the form of sodium sulfide in a concentration of about 0.1 to 2 percent by weight, as well as sodium carbonate.
A serious problem with respect to the sodium sulfide in the scrubber water waste is that upon neutralization of the waste liquids, the sodium sulfide can be converted under slightly acidic conditions into hydrogen sulfide, which is a highly toxic and noxious gas with a bad odor. Accordingly, disposal of the scrubber water waste is difficult, because it is initially corrosive, while after neutralization it may give off the toxic and noxious aroma of hydrogen sulfide. Accordingly, it cannot be desirably disposed of in a waterway, or in a landfill, without problems.
Similarly, scrubber water wastes may contain cyanide ion, typically sodium cyanide in a concentration on the order of 0.001 to 0.0001 percent by weight. This highly toxic material creates further problems in the disposal of scrubber water wastes.
Likewise, small amounts of oil are found in the scrubber water waste. The oil requires removal from the effluent for disposal in order to avoid damage to the environment.
In accordance with this invention, a process is provided by which the scrubber water waste is converted from an unwanted material which is highly harmful to the environment if released in raw form, into an essentially sulfide and cyanide-free caustic soda solution which may have commercial value in its own right, so that the method of this application can turn waste material into a valuable industrial product under preferred circumstances.
Alternatively, the scrubber water waste may be utilized while being disposed of to recover dissolved metals in various waste products, such as copper, zinc, and iron, and to convert them into a form where they may be resmelted into valuable pure metal again. At the same time the scrubber water waste may also be used to neutralize acid wastes.